docs: def potentiallayers(self, x, y, layers, aq=None):
          '''Returns array of size len(layers) only used in building equations
          Defined here as it is the particular solution inside a semi-confined aquifer
          and cannot be added by using eigen vectors'''
          if aq is None: aq = self.model.aq.find_aquifer_data(x, y)
          pot = np.zeros(len(layers))
          if aq == self.aq:
              pot[:] = self.potstar[layers]
          return pot